High densities CAMs (Content Addressable Memory) are most widely used for IP lookup-/-packet classifications operations in routers. The CAM circuits consume a good amount of power during lookup operations.
FIG. 1 shows the search operation for a conventional high density CAM. For example, if the size of memory is M words for each of N bits and number of match lines is M then all the M match lines are precharged to vdd-vt through a PRCH_signal. In the worst case, if there is no data match or a hit condition, all the match lines would discharge. If average discharge current through one match line is IMatch then the worst case discharge current is M×Imatch, which takes a heavy toll on the power consumption of the content addressable memory circuit, wherein the searching of each data word takes into account searching through individual CAM cells. However, if a status of validity or invalidity is set for a given word then charging and discharging processes can be avoided for the invalid words in the memory cell.
Thus, a need is felt for a high-density content addressable memory circuit array, which would charge/discharge only for the valid word match lines.